1. Field of the Invention
The present invention is in the technical field of heavy construction related to the installation, repair, and replacement of pipelines. Particularly, the present invention is in the technical field of in-situ replacement methods of existing pressure pipelines such as, but not limited to, drinking water, natural gas, and sewerage. “In situ” is a Latin phrase meaning “in position,” and in this case means the old pipeline is replaced without complete removal or excavation.
2. Description of the Prior Art
Many cast iron pipelines supplying our drinking water and natural gas and carrying away our sewerage are aging, corroding, and generally wearing out. In urban areas where space is tight and buried infrastructure is very dense, buried pipelines are particularly expensive to replace. The general approach in many areas is “run to failure” where leaks and other sometimes-catastrophic failures are repaired only after they occur. A systematic, proactive, and cost effective approach to replace our aging underground pipeline infrastructure is needed. In-situ pipe replacement using a polymer pipe is an economical and proactive solution to replacing old pressurized water, gas, and sewer pipes.
Pipelines fall into two basic groups: gravity flow and pressurized. To extend the useful life of gravity flow pipelines, such as sanitary sewers, rehabilitation techniques have been developed over the past forty-plus years. These techniques save time and money by utilizing a liner to reduce ground water infiltration and thus the treatment demand on sewer plants. The rehabilitation of gravity pipelines is a fairly simple process. A felt tube (or “sock”) is impregnated with a thermo-set resin at a manufacturing facility and stored in a refrigerated facility. The impregnated tube is then transported in refrigerated trailers to a project site where it is installed by water or air inversion (like turning a sock inside out) and then the resin is cured using hot water, steam, or ultra violet light. The result of this process is a rigid, non-structural tube that becomes a liner.
The above process is referred to as CIPP (cured in place pipe) and was invented by Insituform in 1971 and is still widely used today. Because gravity flow pipelines follow a constant grade and alignment and have manholes at regular intervals, installation of CIPP is accomplished without excavation (“no-dig”) by inverting the liner in and between manholes. The primary purpose of this type of rehabilitation in gravity sewers is to prevent ground water from entering the pipeline through the joints and broken pipe, thus preventing it from being conveyed to the treatment plant for processing along with raw sewerage. Treatment plants are the most expensive part of the sanitary sewer disposal process and reducing ground water infiltration saves capacity and money.
The rehabilitation of pressurized pipelines carrying water, sewerage, natural gas, or other materials is more complicated. Pressurized pipelines have no manholes for easy access nor do they follow a constant line and grade (the pressure causes the material to flow and not gravity). They normally follow the natural terrain of the ground in which they were installed. In addition, the pipeline path could vary based on the allowable engineering parameters for the particular piping material and construction method such as allowable deflection at joints or flexural modulus. Finally, pressure pipes have appurtenances attached to them like valves, tees, wyes, elbows, bends, and others which further complicate rehabilitation and replacement.
Over time, the interior of older cast iron water pipes not lined with cement mortar or epoxy become encrusted with various deposits known as tuberculation. It is important to remove tuberculation when it builds up enough to impact both water quality for drinking and water volume for fire fighting. Additionally, soil surrounding an exterior pipe wall may have a chemical composition which causes corrosion, further deteriorating the pipe.
To deal with tuberculation in old cast iron pipes, a process called cement mortar lining was developed to line the interior of water pipelines in-situ. The lines are cleaned and a thin layer of cement mortar is installed using robotic equipment that moves through the pipeline. This process does not add any structural strength to the existing pipe; it only improves water quality and flow. The preparation of pipes for the cement mortar lining process is the current foundation for in-situ pipeline replacement and for pipeline rehabilitation.
The current methods for replacing or rehabilitating water and other pressure lines include: 1) Digging and replacing the existing pipe in the same trench, 2) Installing a new pipe by digging a parallel trench and abandoning the old line once the new line is put into service, 3) Pipe bursting, which is the process of bursting the existing pipe and simultaneously pulling in a new pipe, 4) Traditional slip lining, which is inserting a smaller diameter pipe into the existing pipe, or 5) Installing a structural CIPP (cured in place pipe) liner.
Pipe bursting is well established but expensive as is any version of digging and replacing. Slip lining is simple and straight forward but usually reduces capacity to an unacceptable level because of the reduced diameter of the new pipe. CIPP for water or other pressure lines is expensive, appurtenances are difficult to attach, it may need to rely on the existing pipeline for structural integrity, and it requires a long lead time to install properly.
A viable solution for overcoming these problems is to replace the entire piping system with an in-situ replacement pipeline. This in-situ pipeline utilizes a deformed polymer pipe, such as high density polyethylene (HDPE), and can employ up to 100% of the old pipe's interior, thus having little impact on water flow or volume.
For comparison purposes, to clean and install a cement mortar lining in old water piping requires these steps:
1. Install and test a temporary surface pipeline (by-pass) to serve water users. This by-pass is temperature sensitive and in northern climates, the season is operational from about mid-March to mid-November. The old buried line is then taken out of service and dewatered. Sections of pipe containing valves, tees, bends above about 22.5 degrees, and other obstructions are removed by excavation. The line is then cleaned using mechanical scrapers.2. Spray cement mortar onto the pipe walls using remote controlled spinning nozzles.3. Open any cement mortar covered service connections by blowing air back through the service connection line from the meter vault to the main. If the service lines are galvanized steel or other deteriorated material, they are usually replaced.4. Install new valves, tees and bends to the existing pipe.5. Fill and chlorinate the line and test for pressure loss and pathogens.6. Return the line to service, backfill excavations, restore surface features (roadway, sidewalk, grass, etc.) and remove the temporary by-pass.
For further comparison purposes, to clean and install CIPP lining in old water piping requires these steps:
1. Remove a section of pipe by excavation to determine the inside dimension and measure the length to be installed. Order a liner from the factory manufactured to the specified interior dimension and length. If the liner is too large in diameter, it will create a fold which will weaken the liner. If it is too long, it will be difficult to install. If it is too small in diameter, it may be weakened by not being in contact with the cast iron pipe walls. If it is too short, it will be unusable because it would be impossible to finish the ends.2. Install a by-pass line as described above. In some instances, certain bends may not require removal depending on their degree and radius.3. Wet out and transport the liner to the site and install using air or water inversion. To reopen the service connections, cut and remove the liner covering the service connection with remote control cutters.4. Seal the liner to the existing pipeline to prevent water from getting between the cast iron pipe and the liner.5. Install new valves, tees and bends to the old cast iron pipe, backfill, and restore.6. Fill, chlorinate and test.7. Return the line to service.
Per the method of this invention, to clean and install an in-situ new pipe in old water piping requires these steps:
1. Install by-pass as described above. Remove valves, tees, bends above about 11 degrees (or another angle as specified by the deformed pipe manufacturer) and all service connections.
2. Install deformed polymer pipe and expand it (reform it to round shape), utilizing up to 100% of the existing pipe's interior diameter.
3. Attach by butt or electro fusing new valves, tees, bends and service connections to the new pipe. Most of these fittings are inexpensive, off-the-shelf, easy to install, and do not rely on the old existing pipeline for reconnection or structural support.4. Fill, chlorinate and test.5. Return line to service.
Millions of feet of cement mortar lining have been installed over the past twenty years; the process is well known, understood and accepted. The major expense of this process comes before and after the application of the cement mortar. Installing a new in-situ pipe inside the existing pipe in lieu of cement mortar lining is a natural evolution in the water pipe replacement process.
The advantages of using the in-situ pipe replacement method of this invention over other methods are:
1. The finished product is a new stand-alone pipe with no reliance on the existing pipe to achieve an acceptable pressure rating or to attach appurtenances. The old pipe is only effectively used as a sleeve that holds back the earth and creates a space for the new pipe during installation.2. Polymer materials like HDPE are widely accepted for a variety of pipeline types and uses.3. Fittings are readily available, inexpensive, and easily heat fused to the new polymer pipe and not installed onto the old pipe.4. The variation in old pipe diameters is overcome by the number of polymer pipe sizes that are available.5. This method creates a new pipeline system with, in most cases, a greater capacity than the pipe it is replacing. This is due to the smoothness of the polymer pipe interior which creates less fiction and lowers pressure loss over distance.6. Cost savings of around one third (33 percent) or greater over other methods.
By deforming the polymer pipe immediately after it is manufactured it can then more easily be inserted into the old pipe and can occupy up to 100% of the old pipe's interior. Making deformed polymer piping is established technology (see Dura-Line Corporation for example) and generally the pipe is factory formed in a u-shape about one half its final expanded diameter. The pipe is then re-rounded in-situ per established methods like heat and pressure. This is important because the deformed size makes installation easier and the expanded size makes obtaining flow easier.
Standard round HDPE pipe comes in three standard sizes: IPS, short for cast iron pipe size; DIPS, or ductile iron pipe size; or metric (imported). Fittings are made to accommodate these standard sizes. In addition to size, HDPE is rated for pressure defined as SDR (often shortened to DR), standard dimension ratio. SDR is the ratio of pipe diameter to wall thickness and the lower the value, the higher the pressure the pipe will withstand. The higher the pressure rating, the thicker the pipe wall is thus reducing the interior diameter. Manning n value is the value by which flow can be compared within various types of pipe walls. For example, the interior wall of smaller HDPE can allow greater flow than the interior wall of a larger unlined cast iron pipe.
Installation of a new deformed pipe is procedurally similar to slip lining (inserting a round, not deformed new pipe into an old pipe) but offers the significant advantage of a larger diameter new pipe with its associated higher flow rate and volume. As an example, to slip line an eight-inch cast iron pipe, the best fit would be a ductile iron pipe size six-inch HDPE pipe (Standard Dimension Ratio of 17) with an outside dimension of 6.9″ and interior dimension of 6.04″. Even with the reduced Manning n value of the HDPE material, the result is a significantly lower flow because of the smaller diameter of the new pipe. The deformed and reformed in-situ process with the same pressure rating of 125 psi would be an eight-inch outside dimension with a 7.04-inch interior dimension. It should be noted the difficulty factor of using a 6-inch HDPE pipe to slip line eight inch cast iron pipe is extremely high and would seldom, if ever, be attempted in real field conditions. This example was given for illustration purposes; in reality, the best a contractor could expect to install is a six-inch iron pipe size pipe with an interior dimension of 4.9 inches
Although flexible liners can achieve the same volume and flow, new fittings must be attached to the old pipe and not to the flexible liner. Also, the flexible liner in some cases must rely on the existing pipeline for structural integrity. The in-situ method of this invention creates a new pipeline that does not rely on the old pipe in any way after the new installation. The new pipe is structurally independent and all fittings are attached only to the new pipe. Special transition pieces are used where the new pipe exits from the old to allow the use of standard fittings such as valves, bends, tees, etc.